1. Field of the Invention
The present invention relates to a touch panel for a display device, which is disposed close to a display surface of a display device, such as a liquid crystal display device, and which outputs a predetermined signal corresponding to a position at which an operator presses on a panel surface with a pen or a finger based on information displayed on the display surface.
2. Description of the Related Art
Since, in this type of touch panel, an area corresponding to the display surface of the display device can be used for both displaying and inputting information, the utilization factor of the area is increased, and therefore the touch panel is increasingly demanded for compact information processors and communications equipments, in particular, mobile communications terminals.
FIG. 2 is a sectional view of a conventional touch panel (disclosed in FIG. 2 of Japanese Patent Laid-open No. 2000-187197 A).
As shown in FIG. 2, a touch panel 10A is basically composed of a pair of resistive layers (first and second resistive layers) 12 and 13 disposed opposite to each other across a plurality of insulating dot spacers 11, and a light-transmissible flat plate, for example, a transparent glass plate 16, for protecting the second resistive layer 13 which is laid on the glass plate 16. The touch panel 10A is disposed close to a display device 30 such that the glass plate 16 faces toward the display surface of the display device 30.
In this construction, when the outer surface of the first resistive layer 12 is touched to be pressed, a touched portion of the first resistive layer 12 is brought into contact with a portion of the second resistive layer 13 opposite thereto, and a signal corresponding to the contact position (touched position) is generated.
In a practical construction, a transparent layer, for example, a polyethylene terephthalate (hereinafter referred to as PET) film 15, is laminated on the outer surface of the first resistive layer 12 for protection thereof, so the touching operation is implemented on this PET film 15.
The first and second resistive layers 12 and 13 are combined at their peripheries by means of a sealing member 14 to be dustproof and waterproof.
A light unit is added to the display device 30 to illuminate the display surface brightly for easier observation. A front light unit 20 to shed light on the front face (display surface) of the display device 30 is often used as the light unit in recent years.
In FIG. 2, the touch panel 10A is attached to the display device 30 having the front light unit 20 described above. The front light unit 20 comprises a light source 21 and a light conductive plate 22 disposed facing the display surface of the display device 30 and adapted to guide light emitted from the light source 21 located at an end of the light conductive plate 22 toward the display surface of the display device 30. Light made incident on the display surface is reflected thereat or inside of the display device 30, travels through the light conductive plate 22 and the touch panel 10A, and exits out (refer to an arrow indicated by a broken line in the figure), whereby an image on the display surface is visualized.
The light conductive plate 22 has an array of prisms, whose respective ridges are parallel to one another, formed on a surface thereof opposite to a surface facing toward the display device 30, thereby guiding light, which has come into the light conductive plate 22 through its end face, toward the display surface of the display device 30.
However, in the conventional structure shown in FIG. 2, since the touch panel 10A and the front light unit 20 are constituted discretely from each other, the touch panel 10A is handled individually and easily subjected to vibration and shock during transportation or assembly. And also the touch panel 10A is required to be strong enough against vibration and shock even after mounted on the device body. Therefore, the glass plate 16 is increased in thickness so as to reinforce the touch panel 10A and also to prevent itself from getting damages. However, this gives a disadvantage that the display device 30 has its whole thickness D increased when attached to the touch panel 10A, and also a problem that since the light conductive plate 22 is brought into direct contact with the glass plate 16, the light conductive plate 22 may be damaged or broken by the glass plate 16 when vibration or shock is applied to the touch panel 10A.
Accordingly, a touch panel for a display device (as shown in FIG. 1 of the above-described Japanese Patent Laid-open) was disclosed, where, as shown in FIG. 3, a second resistive layer 13 of a touch panel 10B is in close contact with a surface of a light conductive plate 22, on which an array of prisms are formed.
In this touch panel, a member (the glass plate 16 in FIG. 2) interposed between the light conductive plate 22 and the second resistive layer 13 of the touch panel 10B is eliminated, and the touch panel 10B is integrated with a front light unit 20, and thus the whole thickness D can be reduced when the touch panel and the front light unit are attached to a display device 30. Further, the glass plate 16 in FIG. 2 is not present, and this solves the problem that the light conductive plate 22 is damaged or broken by the glass plate 16 when vibration or shock is applied to the touch panel 10B.
Furthermore, the present inventors proposed countermeasures to overcome the problems of the touch panel disclosed in FIG. 2 of the above-mentioned Japanese Patent Laid-open, and disclosed the details thereof in Japanese Patent Application No. 2000-387641 that was filed on Dec. 20, 2000 and has not been open to the public (therefore, the related invention in the Japanese Patent Application does not constitute prior art under 35 U.S.C. xc2xa7102). In short, as shown in FIG. 4, a layer of a transparent gel material with a low refractive index 17 (17b) is disposed between a glass plate 16 and a light conductive plate 22, whereby vibration or shock applied to a touch panel 10C can be absorbed, the glass plate 16 can be made thinner, and visibility of reflected light from a display device 30 can be secured. In addition, as shown in FIG. 5, a touch panel 10D is also disclosed in which a layer of a transparent gel material 17 (17c) and a transparent film 19 made of a material with a low refractive index are disposed between a glass plate 16 and a light conductive plate 22 thereby obtaining a similar advantage.
However, there is a problem described below in the conventional touch panel shown in FIG. 3.
Since the second resistive layer 13 is in close contact with the surface of the light conductive plate 22, on which the array of prisms are formed, as described above, the second resistive layer 13 is uneven corresponding to the surface of the array of prisms, and insulating dot spacers 11 are interposed between the uneven second resistive layer 13 and a flat first resistive layer 12.
Accordingly, it becomes difficult to secure the linearity of resistance value at each position on a touch panel operation surface (the PET film 15), and errors occur easily in positional information obtained.
In addition, this makes it difficult to dispose individual insulating dot spacers 11 with an even height on the second resistive layer 13, whereby the PET film 15 constituting the touch panel operation surface tends to undulate deteriorating display quality.
Furthermore, this gives a problem that, with a long term use, protrusions on the array of prisms of the light conductive plate 22 and protrusions on the second resistive layer 13 covering the light conductive plate 22 are liable to damages, resulting in inferior durability.
Still furthermore, in the touch panels shown in FIGS. 4 and 5, the transparent gel material 17 (17b) with a low refractive index and the transparent film 19 made of a material with a low refractive index have not been so fully developed as to be adapted for mass-production yet. As a result, to date, the touch panels have not been introduced on the market inexpensively and massively.
In addition, a problem is pointed out that light, which is directed toward the display device 30, reflected at the display surface or inside thereof, and supposed to pass through the light conductive plate 22 and the touch panel 10C or 10D to finally exit out, is reflected at the glass plate 16, thereby diminishing an amount of light exiting outside, and resultingly deteriorating the visibility of the display surface of the display device 30.
The present invention is made to overcome these problems in the aforementioned touch panels, and its object is to provide, inexpensively in a large quantity, a touch panel for display device, which combines the advantages of each of the touch panels shown in FIGS. 2 to 5. Specifically, the touch panel is structured such that the whole thickness is not increased substantially when attached to the display device, the light conductive plate is not damaged by the light-transmissible flat plate when subjected to vibration, errors do not come out in obtained positional information, the operation surface does not undulate, the display quality does not deteriorate, and that the durability is excellent.
Another object of the present invention is to effectively inhibit light, which is reflected at the display surface or inside of the display device, from being reflected at the touch panel, thereby preventing the visibility of the display surface from deteriorating.
In order to solve the above problems, a first aspect of the present invention provides a touch panel for a display device, which is structured such that one of a pair of resistive layers disposed so as to face each other and to sandwich a plurality of insulating dot spacers is laid on a light-transmissible flat plate formed of a PET film, which is disposed close to a display device such that the light-transmissible flat plate faces toward a display surface of the display device and that a front light unit comprising a light source and a light conductive plate to guide light emitted from the light source toward the display surface of the display device is interposed between the light-transmissible flat plate and the display device, and in which an outer surface of the other resistive layer of the pair is touched to be pressed thereby generating a signal corresponding to a position touched, wherein a transparent cushioning member composed of a shock-absorbing layer and a base layer for supporting the shock-absorbing layer is disposed between the light conductive plate and the light-transmissible flat plate.
According to a second aspect of the present invention, in the touch panel of the first aspect, the cushioning member is a PET film having a transparent gel layer.
According to a third and fourth aspects of the present invention, in the touch panel of the second aspect, the PET film is an anti-reflection (AR) film and a low reflection (LR) film, respectively.
According to a fifth and sixth aspect of the present invention, in the touch panel of the first aspect, the cushioning member is structured such that a liquid or gel cushioning material is applied on the touch panel and that a surface of the cushioning material is hardened to eliminate stickiness thereby constituting a base layer.
According to a seventh aspect of the present invention, in the touch panel of the first to sixth aspects, the base layer has a thickness of 10 to 500 xcexcm.
According to an eighth aspect of the present invention, in the touch panel of the first to seventh aspects, the shock-absorbing layer has a thickness of 50 to 500 xcexcm.
According to a ninth aspect of the present invention, in the touch panel of the first to eighth aspects, a gap of 10 xcexcm to 1 mm is provided between the cushioning member and the light conductive plate.
According to a tenth aspect of the present invention, in the touch panel of the first to eighth aspects, the cushioning member is in contact with the light conductive plate.